1. Field of the Invention
The present invention refers to a current amplifier, and a drive circuit for controlled edge power elements comprising a current amplifier in accordance with the present invention.
2. Description of the Related Art
In the current, amplifiers normally used the consumption of current is constant irrespective of the current supplied at the load and equal to the maximum current foreseen.
We now refer to FIG. 1 which shows a current amplifier of the open-loop type according to the known art. It comprises a transistor M1 having the source connected to the supply voltage Vcc, the gate and the drain connected together and connected to a current generator Ibias in turn connected to ground. The gate of the transistor M1 is also connected to the gate of a transistor M2 and to the gate of a transistor M4. The transistor M2 has the source connected to the supply voltage Vcc and the drain connected to the input terminal In of the current amplifier. The drain of the transistor M2 is also connected to the drain and to the gate of a transistor M3, whose source is connected to ground. The transistor M4 has the source connected to the supply voltage Vcc and the drain connected to the output terminal Out of the current amplifier and to the drain of a transistor M5, whose source is connected to ground and whose gate is connected to the gate of the transistor M3.
In this circuit all the transistors operate and a variation of the current applied at the input In becomes amplified at the output Out.
We now refer to FIG. 2 which shows a current amplifier of the closed-loop type according to the known art. It comprises a transistor M5 having the source connected to the supply voltage Vcc, the drain connected to the drain and to the gate of a transistor M7 whose source is connected to ground. The gate of the transistor M5 is connected to the gate and to the drain of a transistor M1 whose source is connected to the supply voltage Vcc. The gate of the transistor M1 is connected to the drain of a transistor M3 whose source is connected to a current generator Ibias, in turn connected to ground, and whose gate is connected to the input In of the current amplifier. The source of the transistor M3 is also connected to the source of a transistor M4, whose gate is connected to the input Ref of the current amplifier and its drain is connected to the gate and to the drain of a transistor M2 whose source is connected to the supply voltage Vcc. The gate of the transistor M2 is also connected to the gate of a transistor M6 and to the gate of a transistor M9. The transistor M6 has the source connected to the supply voltage Vcc and the drain connected to the input terminal In of the current amplifier and to the drain of a transistor M8, whose source is connected to ground. The transistor M9 has the source connected to the supply voltage Vcc and the drain connected to the output terminal Out of the current amplifier and to the drain of a transistor M10, whose source is connected to ground. The transistor M10 has the gate connected to the gate of the transistor M8 and to the gate of the transistor M7.
Also in this circuit all the transistors operate and an unbalancing of the current applied to the input In is amplified at the output Out.
An embodiment of the present invention provides a current amplifier that does not have the inconveniences of the known art and that it is of simple construction.
The current amplifier comprises an input branch having a first input; an output branch coupled to the input branch; and a bias branch suitable for biasing the input branch. The input branch comprises at least one switch commanded by a first bias voltage supplied by the bias branch so as to substantially block the current flowing in the input branch and consequently substantially block the current flowing in the output branch when the current applied to the first input is null.
Another embodiment of the invention is directed to a drive circuit for controlled edge power elements comprising: a first integrating circuit having a first input suitable for receiving in input a first drive signal; an integrating capacitor coupled to the integrating circuit; a first power element driven by the first integrating circuit and suitable for driving a load, the load having a first terminal; characterized in that the first integrating circuit includes a first current amplifier in accordance with claim 1 and that the integrating capacitor is coupled between the first input and a predetermined reference voltage.
The characteristics and advantages of the present invention will appear evident from the following detailed description of an embodiment thereof, illustrated as non-limiting example in the enclosed drawings, in which: